Tail pipe or afterburning control for turbojet engines



Jan. 22, 1957 T. J. n-loMPsoN TAIL PIPE OF AFTERBURNING CONTROL FORTURBOJET ENGINES Filed June 5, 1 948 3 Sheets-Sheet 1 .Jim

T. J. THOMPSON Jan. 22, 1957 TAIL PIPE oF AFTERBURNING CONTROL FORTuRBoJET ENGINES Filed June s, 194e sheets-sheet 2 m Z 4 M H E /y 7 l 5@4J .w 2 E 6 1w 2 I Mx d y Jan. 22, 1957 T. .1. THOMPSON 2,778191 TAII-PIPE OF AFTERBURNING CONTROL FOR 'TURBOJET ENGINES Filed June 3, 1948 3Sheets-Sheet 5 IN V EN TOR.

TAIL PIPE R AFIERBURNING CONTROL FOR TURBOJET ENGINES 19 Claims. (Cl.6035.6)

Ind., assignor to Ben- South Bend, 1nd., a corpo- This invention relatesto turbojet engines for aircraft, and is particularly concerned withmeans for obtaining thrust augmentation in such engines by burning fuelin the tail pipe or tail cone section of the engine. This method ofobtaining thrust augmentation is commonly termed tail pipe burning orafterburning; in the following description and claims, the termafterburning will be more commonly used for the simple reason that it isthe shorter or more condensed of the two terms, although perhaps lessapt.

In such systems, a variable area reaction or nozzle jet is employed andit is desirable to coordinate the rate of feed of the afterburning fuelwith the rate of change of the jet nozzle area for maximum engine thrustefficiency; and an object of the present invention is to provideimproved means for accomplishing this result.

Other objects include:

To provide an afterburning system for turbojet engines wherein there isa minimum of interference with normal engine operation;

To provide improved means for insuring ignition of the afterburningfuel;

To coordinate the rate of feed of the afterburning fuel with the normalsupply to the burners; To provide improved means for operating thevarious controls hydraulically;

And to generally improve the eciency and operating characteristics ofafterburning systems for turbojet engines.

Certain features illustrated and described herein but not claimed formthe subject matter of a copending application by Frank C. Mock, SerialNo. 25,828, filed May 5, 1948, now Patent No. 2,736,166, commonassignee.

In the drawings:

Figure l is a schematic view of a turbojet engine and coacting tail pipeor afterburning control in accordance with the invention;

Figures 2, 3 and 4 are enlarged views in sectional diagram of parts ofFigure l, namely the main fuel control, the afterburning fuel meteringunit, and the jet nozzle area corrector; and

Figure 5 is a sectional schematic of a modification directed primarilyto the means for coordinating jet nozzle area and fuel feed.

The turbojet engine shown more or less diagrammatically in Figure 1 andgenerally indicated at 10 includes a group of burner units or combustionchambers each made up of an outer casing 11 in which is mounted a flametube 12, the walls of which are formed with a series of openings 13 foradmitting air thereinto from the space 12'. A series of air adapters orheaders 14 are detachably connected to the front end of the burnerassembly to direct air under pressure to the space 12', where part ofthe air enters through the holes 13 and mixes with the fuel dischargedfrom burner nozzles 15 (one for each ame tube) to effect combustion, theexpanded air and products of combustion being discharged from the saidtubes through stator blades 16 and turbine blades 17', the latter form-'29,778,191 Patented Jan. 22, 1957 ing part of a turbine rotor 17.generally indicated at 18; it is shown as being of the centrifugal typebut may, of course, be of the axial ow type; it is driven from theturbine and is shown mounted on a shaft 19 common to the turbine rotorand compres sor.

Beyond the turbine is the tail pipe 20; it carries a diffuser cone Z1 atits entrance end and other parts to be described, and at its outlet endterminates in a reaction jet or jet nozzle 22, the area of which isadjustable by means of a pair of gate valves 23 and 24 mounted onsuitable bearings such as trunnions or short shafts 25 and 26. Alsosecured on said shafts are intermeshing segmental gears 27 and 28. Anarm 29 is secured at one end on the shaft 26 and at its opposite end isconnected to a servo piston which is operated in a manner to bedescribed.

The various accessories which go to make up the complete power plant areusually mounted at the front of the engine and in part housed by asuitable streamlined casing 30. To more clearly bring out the featuresof the invention, however, the afterburning fuel metering system andcoacting controls are removed from the housing and illustrateddiagrammatically in operative relation to the engine 10.

Since in Figure l the main fuel supply system is (as an alternate form)functionally related to the afterburning fuel metering device,sufficient parts of the main fuel control, indicated at 4t) in Figure 1,are shown in sectional diagram in Figure 2 to provide an operativedevice. This device is, however, similar to that shown in a copendingapplication of Frank C. Mock, Serial No. 716,154, filed December 13,1946, and for a more detailed showing and description thereof, referencemay be had to said application. Briefly, fuel is supplied to the deviceby way of conduits 41, 42 (see Figure 1), 42 and 43, the fuel beingmaintained under pressure by fuel pump 44. Fuel enters chamber 45, seeFigure 2, where its maximum pressure is determined by a relief orby-pass valve 46 having connected thereto a diaphragm 47, the latterbeing subjected on one side to incoming fuel pressure at chamber 48 andon its opposite side to the force of a substantially constant ratespring 49 in chamber 50 plus metered fuel pressure by way of conduit 51.Thus, valve 46 will open when the pressure in chamber 45 increases to apredetermined value above metered fuel pressure as determined by spring49 and by-pass fuel back to the low pressure side of pump 44 by way ofconduit 52.

From chamber 45, Figure 2, fuel flows to chamber 53 across regulatorvalve 54. This valve is positioned as a function of engine speed andentering air density; its purpose is primarily to maintain a meteringhead across the throttle valve which varies with variations in enginespeed, so that during acceleration of the engine, irrespective of howquickly a pilot or operator may open the throttle valve, the rate offuel feed will be maintained within a predetermined upper limit toprevent dangerously high burner temperatures. When the engine is inoperation, the valve 54 is urged in a valve opening direction by meansresponsive to changes in engine speed; in this instance by a centrifugalgovernor 55 which is mount ed on a hollow shaft 56 having a drive pinion57 secured on the outer end thereof adapted to be driven from theengine. The governor 55 is operatively connected to the valve 54 bymeans of a sliding sleeve 58 and lever 59 pivoted or fulcrumed at 60. Itits lower end, lever 59 engages a member 61 secured on the adjacent endof the stem of valve 54. The opposite end of the said stem is connectedto a diaphragm 62 having on one side the chamber 53 and on the oppositeside a chamber 63.

A throttle valve is shown at 65, it controls a metering restriction 66through which fuel may ow from chamber A dynamic compressor is 53 tochamber 67 and thence across fuel shut-off valve 68 to metered fuelconduit 69. The throttle valve 65 is secured on a slidable rod or shaft70 which at its inner or right-hand end carries a contact head or disc71 engaged by a centrifugal governor '72 rotatable with the enginedriven shaft 56. As this governor swings outwardly with an increase inengine speed, it tends to slide rod 70 to the left and close valve 65against the tension of a governor spring 73, the latter being adjustedmanually from the pilots cockpit by suitable control linkage, includinglever 74.

When the pilot wishes to accelerate, he moves lever 74 to the right orcounterclockwise. This opens the throttle valve 65 and simultaneouslysets the governor spring 73. The engine now speeds up due to an increasein the area of the feed restriction 66 and a corresponding increase inthe rate of fuel feed. However, the speed of the engine cannot increasefaster than a predetermined rate due to the fact that the metering headacross the throttle valve is determined by the regulator valve 54, whichin turn is positioned as a function of engine speed. When the governor72. balances the setting of the governor spring 73, an equilibriumcondition is attained and the engine operates at a steady speed. Todecelerate, the pilot rotates lever 74 to the upon the reverse of theforegoing ensues. The spring '75 in back of the regulator diaphragm 62is for maintaining a minimum metering head; it has little effect on fuelflows above idle.

Upon a decrease in the density of the air flowing to the engine, lessfuel is required to drive a turbine and compressor at a given speed, andunless the maximum rate of fuel delivered to the burners duringacceleration is correspondingly reduced, much higher burner temperatureswill be experienced during acceleration at altitude than would be thecase at sea level under similar engine conditions. A density controlcircuit is therefore provided; it comprises a control jet or fixed floworifice 76 between the chambers 53 and 63, a variable orifice 77 throughwhich the fuel must pass from chamber 63 to a chamber 7S and thence byway of a duct or pasage 79 to the metered fuel chamber 67. The orifice77 is controlled by a needle valve S0 which at its lower end isconnected to a lever or arm 81 secured on the inner end of a shaft S2,rotatable in response to movement of a capsule or bellows S3, mounted ina chamber 8d vented to ram pressure and temperature and having itsmovable end connected by means of a rod or linlr 85 with a lever 86secured on the outer end of the shaft 32. rfhe bellows or capsule S3 isloaded to render it responsive to changes in both pressure andtemperature, see Patent No. 2,376,711 to Frank C. Mock for a method ofloading a bellows for such service. Expansion of the bellows (decreasein density as by a gain in altitude) moves the needle 8G downwardly andenlarges the area of orifice 77; and contraction of the bellows(increase in density) has the opposite effect. lt will be seen that theduct or passage 79 by-passes the throttle valve 65.

For a given engine or turbine speed, the differential across themetering head diaphragm 62 will be constant, and hence the flow throughthe control jet 76 will remain constant. All ow of fuel through the jet76 will pass through the variable orifice 77 in series therewith, andhence the drop across the latter orice will vary as the square of itsarea; and for a lixed or given position of the needle E@ (constantdensity) the drop across the variable orifice 77 will be proportional tothe drop across the control jet 76. The sum of the drop across thevariable orifice 77 and the drop across the diaphragm 62 (or iet '76) issubstantially equal to the drop across the governor valve 65, and at agiven density, the total drop will be proportional to the square ofengine speed. if the effective area of orifice '77 is enlarged, therewill be a corresponding decrease in the drop `across 'this orifice and areduction in head across the governor valve 465, resulting left orclockwise, wherein a diminishing ow of fuel lto and through the lconduit69 and hence to the burner nozzles for a given area of the feedrestriction 66. Thus, if the governor valve is opened for accelerationat a given altitude, less fuel will be supplied to the burners thanwould be the case at ground level or at some lower altitude.

The afterburning or tail pipe fuel is metered by the device indicatedgenerally at in Figure l and shown in sectional diagram in Figure 3. Afuel pump 91, Figure l, has its low 'pressure or inlet side arranged toreceive fuel from conduit 41 and deliver it under pressure throughconduits 92 and 93 to chamber 94, Figure 3, at the intake or receivingend of the `device 90. Fuel in the chamber 94 is maintained at apredetermined pressure over and above metered fuel pressure by means ofa by-pass or relief valve 95 having a stem connected to a diaphragm 96backed by a substantially constant rate spring 97 located in a chamber98, the latter being vented to metered fuel pressure by way of a conduit99. Should the pressure in the chamber 94 'increase beyond apredetermined value, the valve 95 opens and luy-passes fuel back to thelow pressure conduit 42 (Figure l) by way of ports 100, chamber 161 andconduit 102. Thus, the valve 95 sets up the pressure drop across theentire device 91B.

From the chamber 94, Figure 3, fuel flows into valve chamber 193 andthence through ports 104 across a regulator valve into regulator chamber106. The valve 105 is provided with a stem 107 which is connected to apair of diaphragms 1R13 and 109 for a purpose to be described. From thechamber 106, the fuel ows by way of a passage 11d and valve chamber 11dacross a metering or throttle valve lll, shown in the form of a hollowpiston, which controls the ilow of fuel through metering restrictions112 formed in a cylindrical sleeve 113, the said piston valve 111 beingmounted to reciprocate in said cylinder. The piston valve 111 isconnected by a stem or rod with a servo or actuating piston 111', thefunction of which will presently be described. A spring 114 normallyurges the pistons 111, 111 in a valve closing direction, which is towardthe right in Figure 3.

Metered fuel owing through the restrictions 112 passes into chamber 115and thence flows by way of conduit 116 to an afterburning fuel manifold117, note Figure l, whence it is discharged through any selected numberof discharge nozzles 11S into the chamber 119 of the tail pipe 20. Eachnozzle is preferably located directly in the lee of a diffuser or jetbar 120, formed with an active surface contoured in a manner such as tocause the fuel discharged thereagainst to adhere thereto and then spreadlaterally and also radially inwardly to the edges of the bar, where thefuel is caught by the gases flowing at high velocity through the tailpipe and diffused throughout the chamber 119. Ffhese bars not only serveto act as effective diffusers of the fuel, but they also permit the fuelmanifold 117 and discharge nozzles 11S to be located exteriorly of thetail pipe out of the heat zone, thereby avoiding cracking andearbonization of any residual fuel which may remain in the manifold andnozzles after the tail pipe burning system is shut down, and which mightotherwise result in clogging of the fuel system at this point. The saidjet bars 120 are more fully illustrated and described in the copendingapplication to Mock, Serial No. 25,828, heretofore noted; they form nopart of the present invention.

Reverting now to Figure 3, thc metered fuel in chamber 115 may also passthrough port 121 into a chamber 122 and thence by way of passage 123into chamber 124 on the right-hand side of the diaphragm 10S. Thediaphragm 108 is thereby subjected on the one side to the pressureofunmetered afterburning fuel and on its opposite side to the pressure ofmetered afterburning fuel, and the resultant differential is balancedagainst a similar fuel differential transmitted from the main fuelcontrol il and applied across fthe diaphragm 109.Accordingly,'unnictered fuel from chamber 53 of the main fuel controldevice is communicated to a chamber 125 on the one side of the diaphragm109`by way of a conduit 126, and metered fuel is taken from the chamber67 of the said main fuel control device by way of conduits 51 and 128and applied to a chamber 127 on the opposite side of the diaphragm 109.By this means, the valve 105 automatically sets a metering head acrossthe valve 111 proportional to the drop across the throttle valve 65 ofthe main fuel control, and since this drop is roughly proportional toair ow, the rate of feed of the afterburning fuel will also be generallyproportional to air flow.

The position of the metering valve or piston 111 is coordinated with theaction of the gate valves 23 and 24, Figure 1, and hence the area of thejet nozzle 22. Reverting to Figure 1, the tail gates or valves 23 and 24are illustrated as being actuated by means of a servo piston 130 mountedin a cylinder 131, defining chambers 132 and 133 on opposite sides ofthe piston 130. The piston is connected to -the lever 29 by means of arod or link 134, the latter at an intermediate point being provided witha pin 135 which engages a slot 136 formed inthe upper end of a servolever 137, the latter extending downwardly and at its lower end beingpivotally connected to a slide valve 138 provided with a valve land 139slidable in a servo valve 140. Hydraulic operating uid under pressure(in this instance fuel) is communicated to the valve 140 by way ofconduits 141, 142 and port 143, the latter being formed in the body ofthe valve 140; and fluid is conducted to drain or other suitable lowpressure area by way of ports 144 or 145 and conduit 146 leading back tothe -main fuel supply conduit 41. From valve 140, fluid under pressuremay be communicated to the chamber 132 of the servo cylinder 131 by wayof port 147 'and conduit 148, and to the chamber 133 of said cylinder byway of port 149 and conduit 150.

The slide 138 of the servo valve 140 is positioned automatically incoordinated relation with the feed of fuel to the afterburning system bythe jet nozzle area control device generally indicated at 151; itcomprises a suitable casing having therein a diaphragm 152 which dividesthe casing into a pair of chambers 153 and 154. The diaphragm isconnected to the servo lever 137 by means of a rod or link 155 and pin156 engaging in a slot 157 formed in said lever. A spring 158, acting ona piston 159 connected to the rod or link 155, normally urges thediaphragm 152 and hence the valve land 139 to a neutral position whereit closes the port 143. The function of the piston will subsequently bedescribed.

A pilots control regulator is generally indicated at 160; it comprises asuitable casing having therein a diaphragm 161 which divides the casinginto chambers 162 and '163. A regulator valve 164 is connected to thediaphragm 161 and controls a port 165. Hydraulic fluid (in this instancefuel) under pressure flows to the chamber 162 by Way of conduit 166 andvalve port 165; and from the chamber 162 it ows by way of conduit 167 toconduit 168. The fluid in the conduit 168 is supplied equally inopposite directions to a chamber 169 defined in part by the hollowpiston 111 of the valve 111, note Figure 3; and is also applied to thediaphragm chamber 153 of the servo valve control 151, note Figure l.Fuel under regulated pressure is taken from the chamber 110' of theafterburning fuel metering device 90 and conducted to the chamber 163 ofthe small regulator 160 on the right-hand side of the diaphragm 161 byway of conduits 170 and 171, compare Figure 3 with Figure l. Thediaphragm 161 is backed by a spring 172 which is adjustable by means ofa lever 173 acting on a plate 174, the said lever being secured on ashaft 175, see also Figure 5 wherein this construction is shown on alarger scale. A manual afterburning control lever 176 and associatedquadrant 177 4are provided, the said lever being secured on a shaft 178which is operatively connected to 6 the shaft 175 by means-0f an arm179, link rodv180 and arm 181. Chamber '162'is vented to the bypassiet'u'r'n conduit by bleed 182 and conduit 183. To briefly explain atthis pointl the operation of the prescheduled fuel metering andcoordinated gate valve Controls, when the manual control lever 176 is tothe right as in Figure l, the thrust effect of the spring 172 ondiaphragm 161 is substantially zero, at which time the pressure inchamber 162 of the regulator unit 160, Figure l, is substantially equalto the pressure in chamber 169 of the fuel metering unit 90, Figure 3.When the said spring is compressed by moving lever 176 to the left orcounterclockwise, the valve 164 opens and (a) the pressure in chamber169, Figure 3, increases, and this overcomes the force of the throttlevalve spring 114, Figure 3, moving the throttle valve piston 111 to theleft and correspondingly opening metering restriction 112, and (b) thepressure in chamber 153 of the jet nozzle area control device 151,Figure 1, simultaneously increases and moves diaphragm 152 t-o theright, opening port 143 of servo valve 140 and admitting iluid underpressure to conduit 148 and chamber 132, whereupon servo piston 130moves to the right and opens gate valves 23 and 24. By properlyCalibrating the springs 114 and 158, a prescheduled rate of fuel feedand coordinated rate of change in jet nozzle area may be obtained.

Since both the rate of afterburning fuel feed and jet nozzle area areinitially fixed by the interconnecting operating means just described,it may become necessary to adjust or correct the value of either or bothfactors at some engine operating condition, to insure maximum eiciencybefore and after the turbine. This corrective action is obtained bymeans responsive to changes from a preselected ratio of ram orcompressor inlet pressure and tail pipe chamber pressure, such ratiopreferably being selected on the basis of maximum thrust with minimumjet nozzle area and no tail pipe burning. Referring to Figures l and 4,a conduit 185, Figure l, receives tail pipe pressure at point 186, whilea conduit 187 receives ram or compressor inlet pressure at a suitablelocation in the incoming air stream. A pair of pressure responsivebellows or capsules 188 and 189, having a predetermined balancedrelation with one another, are mounted in chambers 188 and 189' and areinterconnected by a slide valve 190 having lands 191 and 192 thereon,said lands being movable in a valve chamber 193. Fluid under pressure,in this instance fuel, is admittedto chamber 193 by way of conduit 194and port 194', While fuel to drain or a lower pressure source may escapefrom said chamber by way of ports 195 and 196 and conduit 197. When theservo valve lands 190 and 191 are displaced from a neutral position,they uncover ports 198 and 199, permitting fluid to flow byway ofconduit 198 to chamber 200 in back of the piston 111 of Figure 3, andalso by way of conduit 199 to chamber 201 in back of the piston 159 -ofthe gate valve control unit 151 of Figure l. The chambers 200 and 201are provided with suitable bleeds 202 and 203 to permit properfunctioning of the pistons 111 and 159. A temperature responsive devicein the form of a bellows 204 is provided and is rendered responsive tocompressor inlet temperature by means of a suitable thermal element 204.The bellows 204 carries at its movable end a needle valve 205 whichcontrols a variable orifice 206 between chambers 207 and 208. Air mayescape from chamber 208 to ram or other lower pressure area by way of ableed 209.

rIhe bellows 188 and 189 are vnormally balanced against one another tohold the slide valve 190 in a neutral position for a predetermined ratioor dilferential between compressor intake or ram pressure and interualtail pipe pressure beyond the turbine, and should this ratio Abecomeunbalanced, the servo valve lands 190and 191 will be displaced andmodify the respective pressures in climber 200, Figure 3, and/or chamber201, Figure l. This-will result in either or both a change in themetering rate of the afterburning fuel and/or a change in the jet nozzlearea. In this manner, it becomes possible to override the initiallycorrelated afterburning fuel metering and jet nozzle area controls andobtain the required corrective action.

The temperature bellows 2M serves to maintain the ratio of tail pipechamber to ram pressure constant. lt does this by varying the effectivetail pipe chamber pressure in bellows chamber S as a function ofentering air or compressor inlet temperature. Since the pressure dropacross the compressor and turbine varies substantially with variationsin entering `air temperature, a preselected fixed ratio of pressures atthe two points specied may be maintained under varying operatingconditions by modifying the effective tail pipe pressure in proportionto changes in the entering air temperature. To insure ignition of theafterburning fuel, means are provided for increasing the rate of fuelfeed to any selected one or more of the burners 12 to project a spurt offlame outwardly through the turbine into the tail pipe chamber 119. Thisis done by unbalancing the fuel feed to the remaining burners. ln thismanner, the overall burner temperature and pressure is maintained at agiven value even though the temperature and pressure in one or moreselected ignition burners is increased during the ignition period.Referring to Figure l, an ignition fuel chamber 215 is provided and maybe communicated with the main fuel conduit 69 by way of a valve port216, controlled by a solenoid valve 217, actuated by a solenoid 218, thewinding of the latter being electricaldy connected by means of a circuitwire 219 and contact 220 with a switch 221. When the switch 221 isclosed, current may flow from the positive terminal of a battery 222 byway of wire 223, switch contacts 224 and 220,

and wire 219 to the coil or winding of solenoid 218. En-

ergization of -the solenoid raises the valve 217 and opens port 216,whereupon fuel may flow from the main fuel conduit 69 into the chamber21S. In Figure 1, the chamber 215 is shown as supplying two of theburners 12 with fuel by way of conduits 225 and 226, fuel manifold 227and nozzles 22S. Since the ignition fuel is taken from the metered fuelconduit 69 of the main fuel control device which supplies fuel to theburners 12 at a constant rate for a given throttle position, there willbe no increase in the rate of flow to engine speed when the valve tionsystem is placed in operation. However, the temperature will rise in theignition burners and each will project a spurt of ame outwardly into thearea of the tail pipe chamber where the afterburning fuel is beingdischarged by the nozzles 118. The switch 221 may be controlled eithermanually or automatically.

The afterburning ,system may be placed in operation by moving the manualafterburning control lever 176 to 217 is opened and the ignithe left orcountercloekwise, as heretofore noted, but it is preferred to have meansfor selectively rendering the afterburning fuel pump 91 effective topressurize fuel to the fuel metering device or regulator 90, the pilotsregulator device 16) and servo valves 140 and 190 prior to actuallystarting the afterburning system. Accordingly, the pump 91 has a by-passline 23) controlled by a solenoid valve 231 adapted to engage in a seat232. A spring 233 normally urges the valve 231 toward .open position; itis closed by energizing solenoid coil 234, which is adapted to beconnected to the positive terminal of battery 222 by wire 23S throughparallel switches 236 and 237. rDhe switch 236 is of the sliding contacttype, closing when the lever 176 is moved a predetermined distancetoward the left from its ineffective position and `remaining closeduntil said lever is turned back to such position; while the switch 237may be used to close the circuit to solenoid coil 234 when the lever 176is in its ineffective position and thus render the pump 91 eifective topressurize fuel to the .de lees 90 :and 160 and servo 'valves 140 and19.0 preparatory to placing the afterburning system in operathe burnersystem and hence in .i

tion. Pump 91 when by-pass valve 231 is open, puts very littleadditional. load. on the engine and hence may be driven continuously; itmay, however, be driven only when the afterburning system is inoperation, if desired.

The valve indicated at 240 is a positive cut-olf for meteredafterburning fuel; it may be used when the afterburning system is shutdown and at other times for convenience in servicing.

An emergency fuel control is shown in block diagram at 241; it bypassesthe main control 40 through conduits 242 and 243.

The valve indicated at 244 is a selector valve whereby main fuel pumppressure may be continuously applied to the various afterburning fuelcontrols and operating servo valves when the engine is in operationinstead of only when the afterburning system is in operation orpreparatory to placing the latter in operation. When this valve isturned clockwise from the position shown, fuel under pressure may flowfrom the high pressure side of pump 44 to conduit 142 by way of conduit245.

Operation Ordinarily, a thrust augmentation or afterburning system isnot used until the maximum power available has been obtained by anadvanced setting of the throttle of the normal fuel system. Thus, whenthe afterburning system is to be placed in operation, the throttle valve65 of the main fuel control unit 40 would be in its high power position.When the pilot or operator desires to obtain thrust augmentation, hegrasps the control lever 176 and closes the switch 237, whereupon thesolenoid valve 231 closes and the pump 91 operates to pressurize fuelVto the chamber 94 of the control unit 90, the throttle regulator 160andthe servo valves 140 and 190. At about the same time, ,the pilotmoves the ilever 176 counterclockwise, whereupon (a) the switch 236closes, holding the valve 231 closed; (b) the spring 174 of the pilotscontrol unit 160 is compressed and the valve 164 opens, permitting fuelto ow through conduit 167 to 168 from which it is applied equally to thechamber 169 on the right hand side of the piston 111 of Figure 3, and tothe chamber 153 on the left hand side of the diaphragm 152 of the unit151 of Figure 1. Fuel now flows across the piston valve 111, Figure 3,and thence by way of conduit 116 to the afterburner fuel manifold 117,Figure 1, from which it is delivered by the nozzles 118 into the tailpipe chamber 119 in lee of and in part against the active surfaces ofthe jet bars 120; and simultaneously with this action, the diaphragm 152moves to the right and opens servo valve to permit fuel to flow to thechamber 132 of the servo cylinder 131, Figure l, and this causes thetail gate valves 23 and 24 to open and increase the jet nozzle area. Asthe pilot moves the afterburning control lever 176 into operativeposition, he may also close the ignition switch 221, and this opens thesolenoid valve 217 and permits igntionfuel to ow from the conduit 69 tochamber 215 and thence by way of conduits 225 and 226 and manifold 227to the ignition burners, and a spurt of ame is projected outwardlythrough the turbine blades 17 into the afterburning fuel in chamber 119.Since the overall rate of fuel feed to the main burner system is notincreased, the speed of the engine as well as the temperature of themain burner system will not be increased when the ignition fuel issupplied to the ignition burners.

Should the prescheduled rate of fuel feed and jet nozzle area tend tobecome unbalanced, the bellows 183 and/ or 189 will 'become effective tomove the servo valve 190 into a position where it -will act on thepiston valve 111 through conduit 193 and/or on the piston 159 throughconduit 199', in the manner heretofore specified.

To close off the afterburning system, the lever 176 is turned clockwiseto a position such that the dierential across the tliztplfrra grrr 161of the throttle control unit is substantially zero, whereupon there is areduction in pressure in the chamber 169 of the afterburning fuelmetering unit of Figure 3, and the piston valve 111 closes, stopping theow of fuel to the nozzles 118, Figure l; and at the same time thepressure in chamber 153 on the left-hand side of the diaphragm 152 ofthe device 151 of Figure 1 is also reduced, the spring 158 moves theservo valve piston 138 to the left, fuel under pressure flows to thechamber 133 of the servo cylinder or motor 131, and the gate valves 23and 24 are adjusted to the most effective jet nozzle area for normalengine operation. When the lever 176 is moved back to a non-operatingposition, the switch 236 opens and this in turn opens the lay-passconduit 230 of pump 91 and the load on the latter is reduced to a lowvalue.

Instead of metering the afterburning fuel in proportion to the dropacross the throttle valve 65 of the main fuel control 4f?, it may provedesirable to meter such fuel in proportion to the rate of ow of fuel tothe main burner system independently of the main fuel control. Means foreffecting this latter function is shown as an alternate control inFigure l; it consists in disposing a venturi meter 258 in the fuel line69 having one or more orifices 251 formed in the constricted portionthereof and communicating with the conduit 128 by way of a conduit 252and selector valve 253. Another conduit 254 communicates pressureupstream of the venturi 250 with the conduit 126 through selector valve255.

in the position of the selector valves 253 and 255, the venturi meter isclosed off from the lines 126 and 128 and hence the differential acrossthe diaphragm 189 of the afterburning fuel metering unit 9i) of Figure 3is proportional to the drop across the throttle valve 65 as heretoforedescribed. However, by turning the selector valves roughly about 90anticlockwise, the conduits 252 and 254 will be communicated with theconduits 126 and 128 and the latter will be closed off from the mainfuel control unit 40. The differential across the diaphragm 189 thenbecomes proportional to flow of fuel through the conduit 69 squared.

ln a gas turbine compressor engine, airfiow is proportional to enginespeed, and the force set up by theengine driven governor 55 of the mainfuel control 40 of Figure 2 is proportional to engine speed squared.rThis force is therefore proportional to airflow squared and is used toset up a head across the variable metering restriction 66. Since thefuel iiow through said restriction is proportional to the square root ofthe head, fuel fiow as regulated and as corrected for changes in densitybecomes proportional to air ow. Hence, in both methods of producing adifferential across the diaphragm 109 of the after-burning fuelregulator and metering device 96 of Figure 3, fuel iiow to theafterburning nozzles 11S is rendered substantially proportional to airflow. An advantage of the venturi meter arrangement is that it may beused with the emergency control 241, which is not the case when the dropacross the throttle valve 65 is taken as the controlling differential.lf the emergency control has a correction for changes in density, fuelflow would still be proportional to air flow.

Figure illustrates a modification in the afterburning system withrespect to that shown in Figure l. ln the arrangement of Figure 5, themeans for coordinating the rate of fuel feed and jet nozzle areaoperates as a function of engine speed. Also, there is a separate fuelregulator and metering device for the afterburning fuel, which rendersthe afterburning fuel system independent of the main fuel control.

The parts in Figure 5 which correspond to like parts shown in Figures lto 4, inclusive, are given corresponding reference numerals, and need nofurther desciiption.

The afterburning fuel pump 91 is controlled in the same manner as inFigure 1; it delivers fuel to input chamber 261 of an afterburning fuelregulator unit 26d, the metering and throttle control section of whichis substantially similar to corresponding parts of theI unit 96v ofFigures l and' 3. f The delivery pressure'of the fuel in chamber 261 ismaintained at a constant predetermined value over and above metered fuelpressure by means of a. by-pass piston type valve 262 having its sternconnected to a diaphragm 263 backed by a spring 264 in a chamber-265,the latter being vented to the fuel metered fuel chamber by way ofconduit 266. When the pressure in chamber 261 exceeds a predeterminedvalue over and above metered fuel pressure as determined by the spring264, the valve 262 opens and bypasses fuel into chamber 267 and thenceby way of conduit 102 back to the low pressure side of the pump 91. Aregulator valve is indicated at 268; it controls a port 269 throughwhich fuel may flow from chamber 261 into chamber 270. A diaphragm 271forms a movable wall between the chambers 270 and 272. The diaphragm isbacked by a substantially constant rate spring which maintains asubstantially constant differential across said diaphragm. When thethrottle valve or piston 111 is opened, fuel flows from chamber 270through metering restriction 121 across said piston valve and thence byway of conduit 116 to the afterburning fuel nozzle 118 of Figure l.Since the difffferential across the diaphragm 271 is maintainedsubstantially constant, the iiow of fuel to the afterburner nozzles willremain substantially constant for any given position of the piston valve111.

Since less fuel is required to maintain a given thrust or power outputas the density of the air fiowing to fthe engine decreases, it isdesirable to provide density compensation for the afterburning fuel.This is done in the regulator 260 of Figure 5 by means of a densitycircuit and coacting parts including passage 274, valve chamber 275,vari-able orifice 276 controlled by needle valve 277 carried by themovable end of a bellows or capsule 278, responsive to changes inpressure4 and temperature and therefore density, and passage 279 havinga bleed 280 therein. Bellows 278 is located in achamber 278' vented toram or compressor inlet pressure and temperature. Fuel flowing throughthis density circuit by-passes the metering restriction 121. It will beseen that at normal ground level pressures and temperatures, the bellows278 will be in its collapsed position, at which time the variableorifice 276 will be of maximum area. There are in effect two fiowpassages in parallel from the port 269 to metered fuel passage 116; theone consisting of chamber 270and feed restriction 121, and `the othercomprising passage 274, valve chamber 275, variable orifice 276, chamber272, passage 279 and bleed 280. The regulator 260 functions to establisha pressure in chamber 270 which is greater than that in chamber 272 bythe pressure value of spring 273. The diaphragm 271 and spring 273maintain a constant differential across variable orice 276, and hencethe flow through said orifice will increase and decrease as valve 277opens and closes. Since all fiow of fuel through variable orifice 276must also flow through fixed orifice 280, the head across the latterwill increase or decrease'upon opening or closing of valve 277. Thus asbellows 278 expands in response to a decrease in the density of the airflowing to the engine and valve 277 progressively restricts orifice 276,the head causing flow across feed restriction 121 will correspondinglydecrease, resulting in a reduction in ow of fuel to the nozzles 118 for-a given position of piston valve 111.

A speed governor is generally indicated at 281. It comprises a series ofweights 281' rotatable with a shaft 282 provided with a pinion 283adapted to be driven from the engine. A servo valve 284 is connected tothe governor 281 and is mounted to slide in a valve casing 285. Thevalve 284 is provided with lands 286 and 287. Fluid under pressure, inthis instance fuel, flows to the valve casing 285 by way of conduit 288and port 288', and iiuid is released to drain by way of ports 289 and290 and conduit 291. Fuel under pressure may fiow to the chamber 200 inback of the piston 1,11 by way of port 292 and conduit ZZ, and fuelunder pressure may also flow from the valve casing 285 to the chamber201 of the jet nozzle area control device by Way of port 293 und conduit199. The governor 281 is preferably adjustable by means of a lever 294acting on governor spring 295.

ln operation, the pilot compresses the spring 172 of the auxiliarythrust throttle regulating unit 160 in the same manner as described inconnection with Figure l, opening valve 165 and permitting fuel underpressure to flow into chamber 162 and thence by way of conduits M7 andl68 to the chamber 169 in back of the piston lll', whereupon the latter,together with piston 111, moves to the right against the resistance ofthe spring 114 and opens the metering restriction lZl; and at the sametime fuel under pressure also flows by Way of conduit 167 to the chamber153 of the device 151, opening the servo valve 138 and permitting fuelto ovv by way of conduit ifi-S to the gate valve servo piston 113i ofFigure l and open the gate valves 23 and 24.

ln explaining coordination of the rate of fuel feed and jet nozzle areaby means of a device operating as n function of engine speed, let it beassumed that the turbine is operating on the normal pipe burning) withthe area of the jet nozzle set for 100% efficiency. lf now the gatevalves were opened and this area increased, there would be an increasein engine speed due to the fact that there would be a higher drop acrossthe turbine. On. the other hand, should the jet nozzle area be reduceddue to closing of the gate valve, the overall drop across the enginewould be decreased and there would be a corresponding decrease in enginespeed.

Using this as a basis for correlating jet nozzle area and l rate ofafterburning fuel feed, it will be` seen that there will be a likevariation in engine speed should the area of the jet nozzle be increasedat a rate faster than a predetermined or prescheduled rate, and therewould be a corresponding variation in engine speed should the jet nozzlearea be decreased faster than a prescheduled rate.

la the position of the governor 281 shown in Figure 5, it can be assumedthat the engine is operating with jet nozzle area and rate of fuel feedin coordinated relation, since at this time the servo valve 284 is in aposition such that the valve lands 236 and 287 block the ports 292 and2)3. if now the engine speed should vary from its prescheduledcoordinated rate with respect to fuel feed and jet nozzle area, 'theservo valve 284 Will become displaced from its closed position and varythe pressures in either the chamber lidi) of the fuel metering unit orin the chami ber 213i. of the device 153i and adjust the fuel feedand/or jet nozzle area to their prescheduled values.

Although only two embodiments of the invention have been illustrated anddescribed, various changes in the form and relative arrangement of theparts may be made to suit requirements.

l claim:

l. ln a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine, a main fuel controlhaving a variable feed or metering restriction and means for maintainingmetering head across said restriction as a function of engine speed, anafterburning fuel control also having a variable feed or meteringrestriction, and means interconnecting said controls whereby thedifferential across the metering restriction of the afterburning fuelcontrol is maintained proportional to the drop across the meteringrestriction of the main fuel control.

2. ln a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine, a main fuel controlhaving a. rari-able feed or metering restriction and means for,maintaining a head across said restriction varying with burner system(no tail variations in engine speed, an afterburning fuel control alsohaving a variable feed or metering restriction, and means including aregulator valve and coacting pressure responsive means such as adiaphragm subjected to the drop across the metering restriction of themain fuel control.

3. In a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine, a main fuel control formetering fuel to said burners, a metered fuel conduit for connectingsaid fuel control to the burners, an afterburning fuel control having avariable metering restriction, and means for maintaining a head acrosssaid restriction responsive to variations in 'the ow of fuel throughsaid conduit.

4. ln a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine, a main fuel control formetering fuel to said burners, a conduit for metered fuel, anafterburning fuel control provided with a variable metering restriction, and means for maintaining a fuel head across said restrictionincluding a fuel head regulating valve and coacting pressure responsivemeans for controlling said valve subjected to a differential pressurevarying withrvariations in the flow of fuel through said conduit.

5. In a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine, a main fuel control formetering fuel to said burners, an emergency fuel control systernarranged to by-pass said main fuel control, a conduit for metered fuelcommon to both controls, an afterburning fuel control having a variablemetering restriction, and means for maintaining a metering head acrosssaid latter restriction varying with variations in the flow of fuelthrough said conduit.

6. In a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine and adjusting the areaof the jet nozzle to obtain maximum thrust for a given overall rate offuel feed; an afterburning fuel control device having a variablemetering restriction and a throttle valve controlling the area of saidrestriction, first fluid pressure responsive means for operating saidthrottle valve, second fluid pressure responsive means for varying thearea of the jet nozzle, and means under the control of a pilot oroperator for controlling the application of an operating fluid to atleast one of said fluid pressure responsive means.

7. In a system for obtaining thrust augmentation in a turbojet engine byburning fuel in a chambered area after the turbine in addition to thefuel supplied to the burners before the turbine and adjusting the areaof the jet nozzle to obtain maximum thrust for a given overall rate offuel feed; an afterburning fuel control device having a variablemetering restriction, a hydraulically operated throttle valve forcontrolling the area of said restriction, hydraulically operated meansfor varying the area of the jet nozzle, a device for regulating the flowof hydraulic fluid to said throttle valve and said area varying means,and means for maintaining a prescheduled rate of fuel feed and jetnozzle area.

8. A system for obtaining thrust augmentation as claimed in claim 7,wherein said last named means includes a device responsive to variationsfrom a predeter mined ratio of compressor inlet pressure and thepressure in said chambered area after the turbine.

9. A system for obtaining thrust augmentation as claimed in claim 7,wherein said last named means includes a device which operates as afunction of engine speed.

10. ln a system for obtaining thrust augmentation in a turbojet engineby burning fuel in the tail pipe section after the turbine in additionto the fuel supplied to the normal burner system before the turbine andadjusting the area of the jet nozzle to obtain maximum thrust for agiven overall rate of fuel feed; an afterburning fuel control devicehaving a variable metering restriction, a hydraulically operatedthrottle valve for varying the area of said restriction, a valve memberfor varying the area of the jet nozzle, a hydraulic motor for operatingsaid valve member, a servo valve for controlling the flow of operatinguid to said motor, a pressure responsive device for controlling saidservo valve, and means for subjecting said throttle valve and saiddevice to hydraulic operating pressure in predetermined proportion toobtain a prescheduled rate of fuel feed and jet nozzle area.

1l. In a system for obtaining thrust augmentation as claimed in claimwherein there is a manually operable device for regulating the admissionof hydraulic pressure to said throttle valve and said pressureresponsive device.

12. ln a system for obtaining thrust augmentation as claimed in claim10, wherein there are means responsive to variations from a given ratioof compressor inlet pressure and the pressure in the chambered areaafter the turbine for subjecting said pressure responsive device to acorrective action.

13. In a system for obtaining thrust augmentation as claimed in claim 10wherein there is a device responsive to changes in engine speed forsubjecting the application of hydraulic operating pressure to saidthrottle valve and said pressure responsive device to a correctiveaction.

14. In a system for obtaining thrust augmentation in a turbojet engineby burning fuel in a chambered area of the tail pipe section after theturbine in addition to the fuel supplied to the burners before theturbine and adjusting the area of the jet nozzle to obtain maximumthrust for a given overall rate of fuel feed; a nozzle arranged todischarge fuel into said tail pipe chamber, a fuel control device forsupplying fuel to said nozzle, said device being provided with avariable feed restriction and a hydraulically operated throttle valvefor controlling the area of said restriction, a valve member for varyingthe area of the jet nozzle, a hydraulic motor for actuating said valvemember, a servo valve for controlling the ow of hydraulic fluid to saidmotor, a pressure responsive element operatively connected to said servovalve, a throttle regulator for controlling the flow of lluid to saidthrottle valve and said element, and means for coordinating the actionof said throttle valve and said element to obtain a prescheduled rate offuel feed and jet nozzle area.

15. In a system for obtaining thrust augmentation in a turbojet engineas claimed in claim 14 wherein there is a device responsive to changesfrom predetermined ratio of compressor inlet pressure and tail pipechamber pressure which acts to modify the effective action of saidthrottle valve and/or element should the rate of fuel feed and jetnozzle area vary from a prescheduled coordinated relation.

16. In a system for obtaining thrust augmentation in a turbojet engineby burning fuel in a chambered area after the turbine in addition tothat supplied to the normal burner system before the turbine, a fuelcontrol device for supplying afterburning fuel to said chambered area,and means for igniting the afterburning fuel comprising means forincreasing the quantity of fuel supplied to one or more but not all ofthe burners Without varying the overall quantity of fuel supplied to allof the burners to cause a spurt of flame to be projected outwardlythrough the turbine into said chambered area without any substantialvariation in engine speed.

17. In a system for obtaining thrust augmentation in a turbojet engineby burning fuel in a chambered area of the tail pipe section after theturbine in addition to the fuel supplied to the normal burner system, amain fuel control for the normal burner system, a conduit for conductingmetered fuel from said main fuel control to the burners of the saidburner system, means for supplying afterburning fuel to said tail pipechamber, and means for igniting the fuel in said chamber comprising aselectively operable valve member and coacting ilow conduit structurearranged to pass fuel from said metered fuel conduit to a selectedburner of the main burner system constituting an ignition burner, tothereby maintain the overall burner supply constant while at the sametime temporarily increasing the supply to the ignition burner and cause`a spurt of flame to be projected outwardly into said chamber from theignition burner without substantially affecting engine speed.

18. A system as claimed in claim 14 wherein said valve member isactuatable by an electric vsolenoid in circuit with a manually operableswitch accessible to a pilot or operator.

19. A jet-engine combustion system having in combination an elongatedcombustion chamber, a main burner in the combustion chamber, a blowerfor supplying air under pressure to one end of the combustion chamber, aturbine at the other end of the combustion chamber, a jet pipe extendingfrom the last mentioned end of the combustion chamber, an auxiliaryburner in the jet pipe, means for supplying liquid fuel to the auxiliaryburner, a liquid-operated servo-mechanism for determining the quantityof liquid fuel supplied to the auxiliary burner, control meansresponsive to the air pressure at the blower inlet, additional controlmeans responsive to the gas pressure in the jet pipe between the turbineand the auxiliary burner, and a control member responsive to thecornbined action of the two control means for controlling the action ofsaid servo-mechanism.

References Cited in the file of this patent UNITED STATES PATENTS200,405 Mendenhall Feb. 19, 1878 2,238,905 Lysholm Apr. 22, 19412,506,611 Neal et al. May 9, 1950 2,520,434 Robson Aug. 29, 19502,565,854 Johnstone et al. Aug. 28, 1951 2,566,373 Redding Sept. 5, 19512,570,591 Price Oct. 9, 1951 FOREIGN PATENTS 919,004 France Nov. 18,1946

